1. Field of Invention
The present invention relates to a system for processing multimedia data. More particularly, the present invention relates to a system for transmitting and storing the multimedia data.
2. Description of Related Art
Multimedia is comprised of audio-visual data. The visual data is comprised of still pictures and video images. The audio data is comprised of speech data and sound data. In general, the still data images and the speech data are the underlying basis of visual data and audio data respectively, wherein the still data image will not change with time and the speech data has the frequencies, bandwidth and statistical properties characteristic of human voice. The forgoing properties will be useful in processing digital signals.
However, because of the unpredictability of the storage space and the bandwidth limitations of later use when processing the data, in general, before the digital data is being stored or transmitted, the processed (compressed) digital data is decompressed and then compressed again according to the required compression ratio before being stored or transmitted. Thus, the conventional method for processing audio-visual data wastes central processing unit (CPU) resources and degrades the performance of the entire system, and the repetition of processing also deteriorates the quality of the signal so as to distort the multimedia data.
FIG. 1 is a block diagram showing a conventional system for processing multimedia data. As shown in FIG. 1, a primitive signal 102 enters a compressor 104. The compressor 104 converts the primitive signal 102 into a digital data stream 106, wherein the primitive signal 102 may be a digital signal or an analogy signal and the compressor may be an application-specific integrated circuit (ASIC) or a digital signal processor (DSP) chip, which may be dedicated to processing video or audio data. The digital data stream 106 is then transmitted to a compressor/decompressor 112. Furthermore, the compressor/decompressor 112 may be a image processing system, a computer or a server for decompressing/compressing the digital data stream one or more times, wherein the compression ratio of the compression is varied according to the storage space of a next device (for example, a hard disk 114) or the bandwidth limitations of a next path (for example, a wired/wireless network 116 or a network of a cell phone 118). The digital data stream 106 is compressed into digital data streams 120, 122 or 124 to be suitable for transmission through the next path or stored into the next storage, for example, a hard disk 114, a network 116 or a cell phone 118.
FIG. 2 is a flow chart illustrating a conventional method for processing multimedia data. As shown, after the flow starts in Step 202, a primitive signal is received by a compressor in Step 204 and compressed into a single digital data stream in Step 206 by the compressor, and the single data stream is transmitted to a decompressor/compressor in Step 207. The decompressor/compressor then determines the compression ratio of the digital data stream according to the storage space of a next device or the bandwidth limitations of a next path in Step 208. For example, if the digital data stream requires compression with a high compression ratio because of limited storage space of the next device or a limited bandwidth of the next path, the digital data stream is decompressed in advance in Step 210 and then compressed into a digital data stream with a high compression ratio in Step 212. Finally, the digital data stream with the high compression ratio is transmitted or stored in Step 214. Similarly, if a low compression ratio is required, the digital data stream is decompressed in advance and compressed again into a digital data stream with a low compression ratio.
To sum up, future storage space and bandwidth limitations during the signal processing stage are unpredictable. Therefore, after Step 208 of FIG. 2, the processed digital signal has to be restored/decompressed, for example, in Step 210, 220 or 230 and processed/compressed again according to the required compression ratio, for example, in Step 212, 222 or 232, and finally the recompressed digital data stream is stored or transmitted, for example, in Step 214, 224 or 234. The above-mentioned complicated system has a redundant procedure and wastes central processing unit (CPU) resources degrading the performance of the system. Moreover, the redundant procedure on the digital data stream will reduce the quality of the signal and thus distort the multimedia data.